The present invention relates to a method irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same, and a laser irradiation device, and more particularly to a method of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor and a pulse laser irradiation device.
The thin film transistor has an active layer of a polycrystal silicon thin film formed on a glass substrate. The thin film transistor may be used for the liquid crystal display and the contact image sensor or other electronic devices. A laser anneal method has been often used in view of reduction in process temperature and improvement in throughput. A silicon thin film is once formed as a precursor and then an ultraviolet ray pulse laser beam is irradiated onto the silicon thin film for causing crystallization to polycrystalline structure. It is widely used that a linear pulse laser beam is scanned in a width direction perpendicular to the line direction.
The conventional laser beam irradiation method has a problem in low uniformity. An influence of a pulse laser beam edge of the previously irradiated pulse laser beam causes a large variation in crystal grain diameters to be formed in the next laser beam irradiation. A melting state of the thin film by the laser beam irradiation depends upon the thin film crystal structure before the laser beam irradiation. Particularly, when amorphous silicon thin film is used as a precursor, a remarkable variation in melting state may appear on a boundary between the crystal region already irradiated with the laser beam and the amorphous region unirradiated with the laser beam.
FIG. 1A is a diagram illustrative of a variation in energy density over position of a pulse laser beam with a top flat energy density profile to be irradiated onto an amorphous silicon thin film for annealing the same. FIG. 1B is a diagram illustrative of a distribution in crystal grain size over position of a polycrystalline region formed by irradiation of a pulse laser beam with the energy density profile of FIG. 1A onto the amorphous silicon thin film. FIG. 1C is a diagram illustrative of a change of distribution in crystal grain size over position of the polycrystalline region by scanning at a pitch xe2x80x9cxxe2x80x9d the pulse laser beam, wherein the crystal grain size has a minimum size value in the vicinity of the laser beam of FIG. 1B. FIG. 1D is a diagram illustrative of a final distribution in crystal grain size over position of the polycrystalline region after scanned at a pitch xe2x80x9cxxe2x80x9d the pulse laser beam, wherein the crystal grain size varied over position.
FIG. 2A is a diagram illustrative of a variation in energy density over position of a pulse laser beam with a top flat energy density profile to be irradiated onto an amorphous silicon thin film for annealing the same wherein a maximum energy density is beyond a micro-crystallization threshold value of the polysilicon film. FIG. 2B is a diagram illustrative of a distribution in crystal grain size over position of a polycrystalline region formed by irradiation of a pulse laser beam with the energy density profile of FIG. 2A onto the amorphous silicon thin film. FIG. 2C is a diagram illustrative of a change of distribution in crystal grain size over position of the polycrystalline region by scanning at a pitch xe2x80x9cxxe2x80x9d the pulse laser beam, wherein the crystal grain size has a minimum size value in the vicinity of the laser beam of FIG. 2B. FIG. 2D is a diagram illustrative of a final distribution in crystal grain size over position of the polycrystalline region after scanned at a pitch xe2x80x9cxxe2x80x9d the pulse laser beam, wherein the crystal grain size varied over position.
In Japanese laid-open patent publication No. 9-219380, it is disclosed that in order to improve the uniformity of crystal grain size of the polysilicon thin film, a pulse laser beam having a step-like energy density profile is irradiated onto the amorphous silicon thin film. Even the irradiation of the pulse laser beam having the step-like energy density profile onto the amorphous silicon thin film causes variation or change in crystal grain size at the beam edge positions, for which reason it is difficult to obtain the required uniformity in crystal grain size of the polysilicon region.
In the above circumstances, it had been required to develop a novel method of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same free from the above problem, and a laser irradiation device.
method of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor and a pulse laser irradiation device.
Accordingly, it is an object of the present invention to provide a novel method of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same free from the above problems.
It is a further object of the present invention to provide a novel method of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same free from any influence of a pulse laser beam edge previously irradiated.
It is still a further object of the present invention to provide a novel method of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same to obtain a uniformity in crystal grain size.
It is yet further object of the present invention to provide a novel device of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same free from the above problems.
It is a further more object of the present invention to provide a novel device of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same free from any influence of a pulse laser beam edge previously irradiated.
It is still more object of the present invention to provide a novel device of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same to obtain a uniformity in crystal grain size.
It is moreover object of the present invention to provide a novel method of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor free from the above problems.
It is another object of the present invention to provide a novel method of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor free from any influence of a pulse laser beam edge previously irradiated.
It is still another object of the present invention to provide a novel method of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor to obtain a uniformity in crystal grain size.
It is yet another object of the present invention to provide a novel device of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor free from the above problems.
It is further another object of the present invention to provide a novel device of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor free from any influence of a pulse laser beam edge previously irradiated.
It is an additional object of the present invention to provide a novel device of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor to obtain a uniformity in crystal grain size.
In accordance with the present invention, there is provided a method of irradiation of a pulse laser beam having a linear shape and a rectangular shape beam spot onto a non-single crystal semiconductor thin film with scanning the pulse laser beam so that previous and next beam spots are partially overlapped, wherein the laser beam has a beam profile which includes: a first beam profile region having a first energy density which is lower than a micro-crystallization threshold value Ea of an amorphous semiconductor for forming a polycrystallization region; a second beam profile region having a second energy density which is not lower than the micro-crystallization threshold value Ea and is lower than a micro-crystallization threshold value Ep of a polycrystalline semiconductor for forming a first micro-polycrystallization region from an amorphous semiconductor region; and a third beam profile region having a third energy density which is not lower than the micro-crystallization threshold value Ep for forming a second micro-polycrystallization region from a polycrystalline semiconductor region.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.